Copper sulfate absorption mass to remove AsH3, PH3, B2 H.sub.4 and SiH4

ABSTRACT

An absorption mass consists of an oxidic porous carrier substance saturated with CuSO4. The CuSO4 is in the form of a monohydrate or with CuSO4 free from water of crystallization.

BACKGROUND OF INVENTION

The invention relates to an absorption mass consisting of an oxidicporous carrier substance saturated with copper sulfate CuSO₄ which issuitable for the elimination of reactive process gases in theelectronics industry.

The electronics industry makes use of reactive gases in the productionof semi-conductors. Commonly used reactive gases are: arsenic hydrideAsH₃, phosphorous hydride PH₃, boron hydride B₂ H₆, germanium hydrideGeH₄ and silicon hydride SiH₄. These reactive gases are toxic and tendto spontaneous combustion so that they must be effectively eliminated toprevent any negative effects on the environment.

An absorbent for the elimination, for example, of AsH₃ consists of a 60%solution of copper sulfate pentahydrate CuSO₄. 5H₂ O and silica gelwhose residual moisture lies between 10% and 25%, following a dryingperiod of 17 hours at a temperature of 110° C. A disadvantage of thisknown absorbent is its small absorption capacity and low thresholdvalue. The threshold limit value (TLV value), in other words, themaximum admissable concentration of the substance can be used toestablish the threshold value. Both factors mentioned above can easilylead to serious contamination of the environment even when the substancehas been subsequently dump-covered as a precaution. An additionaldrawback is that the absorption front becomes totally blurred so that avisual detection of the degree of exhaustion of the absorption masscontained in a glass tube is more difficult.

SUMMARY OF INVENTION

The invention is, therefore, based on the object of providing anabsorption mass having a substantially increased threshold valuecapacity. Threshold value capacity refers to the absorption capacitybeyond which the threshold values (TLV values) are exceeded.

According to the invention, this increased threshold value capacity isachieved by means of an absorption mass consisting of an oxidic porouscarrier substance which has been previously saturated with CuSO₄ in theform of a monohydrate or with CuSO₄ free from water of crystallization.

DETAILED DESCRIPTION

In accordance with the invention, the saturation is preferably carriedout with CuSO₄ free from water of crystallization. Silica gel andaluminum oxide are particularly suitable as carrier substances.

The absorption masses according to the invention have a highreproducible threshold value capacity. In addition, they also constitutean absorption front which can be readily detected with the naked eye.

Such masses can also be readily used for high concentrations and as aresult of their high threshold value capacity facilitate ultimatedisposal.

The absorption masses according to the invention are produced bysaturating the carrier substance with an aqueous solution of CuSO₄. 5H₂O, drying and dehydration at a temperature between 150° C. and 200° C.at atmospheric pressure.

Less favorable process results are obtained if the above mentionedtemperatures are exceeded. At temperatures above 200° C., CuSO₄ canquickly break down to CuO and SO₂. Dehydration can be quickly andreliably achieved at a temperature of 180° C. with inert gas flushing, aprocess which takes between one and two hours.

Saturation of the carrier substance with CuSO₄ can be carried out, forexample, as follows:

A total of 1250 g of silica gel E (Manufacturers: BASF and Grace) havinga granulate size of 6 mm is saturated with a solution of 1000 ml of hotdistilled water and 641 g of CuSO₄. 5H₂ O, subsequently evaporated in adrying chamber at a temperature of 110° C. and finally dehydrated at atemperature of 180° C. The absorbent can be best used when the pale-bluemonohydrate or better still when the white CuSO₄ free from water ofcrystallization is present. The absorption mass thus produced is thenremoved from the drying chamber and immediately filled into glass tubes.Finally, it is stored, if possible, free from humidity.

The absorption mass is employed at room temperature.

The absorption masses according to the invention can be effectivelyemployed to absorb not only arsenic hydride--with its extremely lowthreshold limit value of 0.01 ppm--but also all other reactive processgases commonly used in the electronics industry. The absorption frontcan be easily and distinctly detected in most of the investigated gaseswithout indicator additive as a result of the indication of the gas perse. The following examples substantiate the advantages of the absorptionmasses saturated with CuSO₄. 5H₂ O according to the invention incomparison with the commonly used absorption masses. In all experiments,the absorption masses were produced as described above and filled into aglass tube measuring 440 mm in length and having an inside diameter of24 mm. The dumping height was 370 mm which corresponds to a weight of150 g and a volume of 167.3 cm³. The gas flow rate was 50 l/hour. Ineach example, the first line refers to the data of a commonly usedabsorption mass and the second line to an absorption mass according tothe invention.

    ______________________________________                                        Example 1                                                                     Elimination of arsenic hydride, AsH.sub.3 : (TLV value: 0.01 ppm)                       Treatment                  TLV                                                duration  temp.            capacity                                 Mass      (h)       (°C.)                                                                          Indication                                                                             (1/kg)                                   ______________________________________                                        CuSO.sub.4 /silica                                                                      17        110     blurred grey                                                                            3.7                                     gel E                                                                         CuSO.sub.4 /silica                                                                       2        180     black    14.2                                     gel E                                                                         ______________________________________                                    

    ______________________________________                                        Example 2                                                                     Elimination of phosphorous hydride, PH.sub.3 :                                (TLV value: 0.01 ppm)                                                                   Treatment                  TLV                                                duration  temp.            capacity                                 Mass      (h)       (°C.)                                                                          Indication                                                                             (1/kg)                                   ______________________________________                                        CuSO.sub.4 /silica                                                                      17        110     blurred grey                                                                            6.3                                     gel E                                                                         CuSO.sub.4 /silica                                                                       2        180     black    25.2                                     gel E                                                                         ______________________________________                                    

    ______________________________________                                        Example 3                                                                     Elimination of diboran, B.sub.2 H.sub.6 : MA (TLV value 10 ppm)                         Treatment                  TLV                                                duration  temp.            capacity                                 Mass      (h)       (°C.)                                                                          Indication                                                                             (1/kg)                                   ______________________________________                                        CuSO.sub.4 /silica                                                                      17        110     none      1.0                                     gel E                                                                         CuSO.sub.4 /silica                                                                       2        180     black    19.5                                     gel E                                                                         ______________________________________                                    

    ______________________________________                                        Example 4                                                                     Elimination of monosilan, SiH.sub.4 : (TLV value 10 ppm)                                Treatment                  TLV                                                duration  temp.   capacity                                          Mass      (h)       (°C.)                                                                          Indication                                                                             (1/kg)                                   ______________________________________                                        CuSO.sub.4 /silica                                                                      17        110     none     immediate                                gel E                                escape                                   CuSO.sub.4 /silica                                                                       2        180     black    24.5                                     gel E                                                                         ______________________________________                                    

These examples show a substantial increase in the threshold limit valuecapacities of the absorption masses according to the invention incomparison to the commonly used absorption masses. In addition to thecited reactive gases, dicyanogen, amine, ammonia, H₂ S and NO₂ can alsobe eliminated with the absorption masses according to the invention butalso of course mixtures of any of the cited gases. After absorption ofS₂, the absorption masses according to the invention but also of coursemixtures of any of the cited gases. After absorption of S₂, theabsorption mass can be regenerated at a temperature of 80° C.

SUMMARY

Reactive process gases used in the electronics industry, in particular,AsH₃, PH₃, B₂ H₆, GeH₄ and SiH₄ can be eliminated by means of anabsorption mass consisting of a porous oxidic carrier substance, forexample, silica gel saturated with CuSO₄ pentahydrate. In order toimprove the absorption effect, the CuSO₄ pentahydrate is dehydrated at atemperature between 150° C. and 200° C. to obtain CuSO₄ monohydrate orCuSO₄ free from water of crystallization.

What is claimed is:
 1. A process to eliminate gases selected from thegroup consisting of AsH₃, PH₃, B₂ H₆, GeH₄ and SiH₄ including the stepsof forming an absorption mass by saturating a porous carrier in the formof silica gel or aluminum oxide with CuSO₄ in the form of monohydrate orCuSO₄ free from water of crystallization, contacting the gases with theabsorption mass, and absorbing the gases in the absorption mass.
 2. Theprocess of claim 1 wherein the forming step includes saturating thecarrier with CuSO₄.5H₂ O, subsequently drying the saturated carrier andthen dehydrating the dried carrier at a temperature between 150° and200° C.
 3. The process of claim 2 wherein the dehydrating step iscarried out at a temperature between 175° and 185° C. for a time periodof from one to two hours.
 4. The process of claim 1 wherein the reactivegases are used in the production of semi-conductors in the electronicsindustry.
 5. The process of claim 1 wherein the CuSO₄ is in the form ofa monohydrate.
 6. The process of claim 1 wherein the CuSO₄ is in theform of CuSO₄ free from water of crystallization.
 7. The process ofclaim 1 wherein the carrier substance is a silica gel.
 8. The process ofclaim 7 wherein the elimination of the gases is visually detected. 9.The process of claim 8 wherein the visual detection is by observing themass becoming darker.
 10. The process of claim 1 wherein the mass isformed by drying at an elevated temperature and then dehydrated at atemperature higher than the drying temperature.